I'd have to say Facebook. It's a great way for me to keep in touch with friends and family and the fact that it reminds me when their birthdays are, is an added bonus! I've tried to get into Twitter but it really doesn't interest me yet!
My vote would go for Facebook..Its user-friendly, comes with multiple applications and serves apt in driving good traffic.
Hello nice question? I like facebook, Google + , Twitter And Youtube these are really rare social networking sites.